🚀 go-pugleaf

Michael <mutk@iprimus.com.au> wrote:
>BTW, the performance isn't twice as great on a SMP system. There is 
>overhead, resulting in SMP system being something less than twice the 
>performance.
>
>
>In a nut shell, a SMP Linux system running on 2X 1800 Athlons will 
>always  be superior to a uni-processor 1800 AThlon machine due to the 
>fact that a typical Linux system has many processes running 
>(Multi-threaded or not). But the performance advantage of 
>multi-threaded app is *much* greater than a single threaded app on a 
>SMP system.

Here's an example.  I compiled the kernel using two different
commands (twice each, to make sure the times were valid).

  >make clean;time make bzImage

The above command ran in 2 minutes and 37 seconds, while

  >make clean;time make -j2 MAKE='make -j2' bzImage

ran in 1 minute 28 seconds.

Basically, by taking advantage of both cpu's the compile was 1.8
times as fast.

We can surmise that if I pulled out 1 cpu, the first command would
probably run 1.01 times as fast, but the second command would not
be any faster than the first (actually, because of all the context
switching, it might slow it down to 1.00 again).

A single cpu machine, compared to a dual cpu machine, will
provide an unnoticable speed increase (that may be measurable),
if and only if only one process is running on the machine.  But
a dual cpu machine can compile the kernel as much as 1.8 times
as fast on a heavily loaded machine.

Whether a dual cpu is cost effective depends entirely on how
often one can actually load it down with enough work to see any
benefit.  And as one poster noted, that is less likely with
today's faster cpu's than it was a few years back.  When running
the X server took up 30% of the cpu power, having 2 cpu's made a
very noticable difference for a single logged in user just in
command line responsiveness.  I haven't tried it, but I suspect
that if I pulled one cpu out of this box I would not notice a
difference in command line response more often than once a week.

Since I commonly do things which heavily load the cpu's, I very
much enjoy the advantages of SMP.  Others might find it a
veritable waste of money!

-- 
Floyd L. Davidson         <http://www.ptialaska.net/~floyd>
Ukpeagvik (Barrow, Alaska)                 floyd@barrow.com